This invention relates to an apparatus for electrochemical precision machining of metallic workpieces which comprises a tool holder for an electrode, an oscillating drive mechanism connected to the tool holder to generate an oscillatory motion of the electrode in the machining direction and a continuously linearly moving feed unit in which the tool holder is arranged and moveably supported in guiding means.
In electrochemical material removal, which is based on the principle of the electrochemical cell, an electrolytic solution flows through the small gap between the workpiece to be machined (anode) and the electrode (cathode) supported by the tool holder. While hydrogen ions are discharged at the cathode, metal ions react with OH ions of the water at the anode under the formation of metal hydroxide compounds settling as sludge. As the tool holder gradually moves in feed motion, metal is removed in an electrochemical process. If the electrode performs both, an oscillatory motion and a feed motion, with a voltage pulse being generated at the time of minimum distance, the precision of the machining process can be enhanced even more, accepting, however, a reduced removal rate. Electrochemical precision machining with oscillating electrode entails, however, the problem that an absolutely linear oscillation of the electrode, i.e. one without or with minimum lateral play, is to be ensured.
In an apparatus for electrochemical precision machining of metals known from Specification EP 1097774 A1, linear oscillation of the electrode is effected by an eccentric drive in which a connecting rod connects the crankshaft of an electric motor to the tool holder. The tool holder is supported, at the top and at the bottom, by means of two diaphragms in a feed unit (quill) performing the feed motion. This type of support enables the tool holder to perform a linear oscillatory motion in the quill. Due to a lateral motion component of the connecting rod tip, it is, however, not possible to guide the tool holder without any lateral play, despite the support in diaphragms. The accuracy of 0.05 mm obtainable with this type of support in the horizontal plane is insufficient for many applications, for example, the manufacture of blisk blades for aircraft turbines. Also, the accuracy of 0.03 mm obtainable in a machining direction does not satisfy the requirements for precision machining. Furthermore, the apparatus described in Specification EP 1097774 A1 is disadvantageous in that, due to the play in the connection of the connecting rod to the crankshaft, it can be set up and operated only in vertical position. In addition, this apparatus is not capable of providing the accuracy required for machining operations to be performed with less precision, but higher metal removal rate, since the position of the connecting rod or the electrode, respectively, cannot be determined or set and, further, the electrode is not lockable. The known apparatuses for electrochemical material removal are further problematic with regard to the sealing of the oscillating mechanism against the aggressive electrolyte.